1. Field of the Invention
The present invention relates to the management of the risks of in-flight collision between aircraft.
2. Discussion of the Background
Risks of collision between aircraft have been taken into consideration very early in the history of air transport owing to the fact that concentrations of aircraft occur naturally in the vicinity of airports. To avert such collisions, according to the first solution devised, aircraft were required to follow strictly demarcated air corridors in which their progress was monitored from the ground by air traffic controllers belonging to air traffic control (ATC) organizations. Air traffic controllers are responsible for a territory in which they organize the circulation of aircraft in authorized air corridors. For the regulation of air traffic, the controllers on the ground have information available on the movement of aircraft above their territory. This information comes from the flight plans of aircraft communicated in advance, real-time measurements by their surveillance radars dispersed over their territory and sound and data exchanges with the crew and navigation equipment of the aircraft. The risks of collision between aircraft are detected on the ground by the air traffic controllers using data in their possession and also in flight by the crews of aircraft who keep a visual watch. However, except in cases of extreme emergency, the initiative for avoidance maneuvers comes under the sole responsibility of air traffic controllers.
Traffic density is constantly increasing in the vicinity of certain airports, and the risks of collision are becoming increasingly a matter of concern. This is why the United States Federal Aviation Administration (FAA) launched a program in the 1960s to create equipment for the automatic detection of in-flight collision risks designed initially for passenger aircraft. This program led to the devising of several successive generations of a system known as the Traffic Collision Avoidance System (TCAS) specializing in the detection of very short-term in-flight collision risks (i.e. risks of collision within less than one minute)
A set of TCAS instruments establishes co-operation between aircraft travelling in the same neighborhood by means of another piece of onboard equipment, the transponder, whose use in the meantime, has become widespread on board aircraft for the transmission, to the ground, of information on the aircraft so as to improve their localization by the air traffic controllers.
A first generation of TCAS instruments that was available towards the 1980s, the TCAS 1 system, worked together with Mode-C transponders originally designed to respond to an interrogation by a special radar placed on the ground, known as an xe2x80x9csecondary radarxe2x80x9d to give a piece of information on the identity and altitude of the aircraft that carried it and also enable a measurement of the distance between said aircraft and the secondary radar and a measurement of the speed of said aircraft, these measurements being based on the propagation time of the radio-electrical signals and the variation of this propagation time from one interrogation to another. When placed on board an aircraft, a TCAS 1 instrument periodically sends interrogation signals to the mode-C transponders of the aircraft moving in the vicinity. It picks up their responses, processes these responses, and deduces their positions in terms of distance and heading, the speeds and the altitude levels of the different aircraft moving in the vicinity of the aircraft into which the instrument is integrated. It places this information at the disposal of the crew by means of a special screen and generates alarms known as Traffic Advisories (TA) when it is detected that aircraft could come close within far too small a distance. The crew of an aircraft equipped with the TCAS 1 is informed of the risk of collision but receives no advice on the nature of the evasive maneuver to be performed. This evasive maneuver cannot be done without reference to the air traffic controller, and only in the vertical plane and within a limit of 300 feet.
A second generation of TCAS instruments which is more efficient, namely the TCAS II generation, is currently available. The TCAS II co-operates with mode-C transponders or mode-S transponders and, in addition to the TA alarms, gives Resolution Advisories (xe2x80x9cRAxe2x80x9d) consisting of instructions to climb or descend at 2,500 feet per minute in order to avoid another aircraft, often with an indication of the descent or climb gradient to be adopted to eliminate the risk of collision. Furthermore, when two aircraft involved in a collision risk are both equipped with TCAS II instruments, their TCAS II instruments work together to prevent any conflict and not give the two aircraft simultaneous and contradictory advice on maneuvers that would not eliminate the risks of collision.
A third generation of TCAS instruments, namely the TCAS III generation, is not being envisaged. This is a generation with higher precision in the assessment of heading positions, paths and speeds of other aircraft obtained by means of a specific directional antenna and improved mode-S transponders which, in their response signals, give the GPS (global positioning system) position and the speed vector of the carrier of the transponder. These TCAS III instruments would furnish advice on RA maneuvers including lateral evasion instructions in the horizontal plane, made possible by the improved precision that is being anticipated.
The congestion of air traffic routes over certain territories, for example in Europe, and the improvement of the precision of the navigation means available to the aircraft following the deployment of the GPS satellite navigation systems such as the American GNSS (Global Navigation Satellite System) or the Russian GLONASS (GLObal Navigation Satellite System) are today leading air-traffic control authorities to consider abandoning the requirement, on certain routes, for aircraft to follow preset air corridors and to consider the granting to aircraft, of a certain degree of liberty in the choice of their route outside airports approach zones and outside certain flight levels. This is the navigation technique known as xe2x80x9cFree Flight.xe2x80x9d In addition to a reduced concentration of aircraft in the sky outside airport approach zones and, hence, a reduction in the risks of collision between aircraft, this technique of Free Flight navigation is likely to enable the following of the great circles track between points of the globe that are not directly linked by a predefined air corridor and for which the following of predefined air corridors necessitates more or less great detours.
The Free Flight navigation technique requires not only that aircraft should be equipped with precise navigation means but also that they should be capable, on their own, of resolving conflicts of traffic with other aircraft giving rise to medium-term collision risks, namely risks of collision within about five to ten minutes, whereas this conflict resolution is the task of air traffic controllers during traffic within predefined air corridors. It can be envisaged that the function of medium-term air collision protection will be fulfilled up board aircraft using the Free Flight navigation technique by means of the latest generations of TCAS instruments by augmenting their sensitivity so as to obtain sufficiently early anti-collision warnings, especially as the main problem encountered with TCAS instruments, namely that of false alarms, does not arise beyond a certain distance from airports.
Although a TCAS instrument with increased sensitivity is able to warn an aircraft carrying using the Free Flight technique of a risk of medium-term collision, namely a risk of collision within five to ten minutes, and warn this instrument that it is up to itself to carry out an avoidance maneuver, it cannot propose the most appropriate modification of the aircraft route and, at most, gives a suggestion of an avoidance maneuver by the top, the bottom, right or left. This simple suggestion of a maneuver, which is well suited to a emergency situation namely that of a collision risk within the next minute, is not suited to the resolution of a traffic conflict where the risk of collision is only a medium-term risk of collision within five to ten minutes.
When it is informed of a traffic conflict generating a medium-term collision risk, the crew of an aircraft has the time to decide on its own on the route modification to be made in order to eliminate the risk of collision, in searching for the avoidance path whose consequences are the least detrimental to the progress of the aircraft mission. In making this search, it will attach greater importance to the shortest possible path diversion at constant speed in the horizontal plane rather than to a change in speed or a path diversion in the vertical plane, both of which are more difficult to manage for the aircraft and more disturbing for the rest of the traffic.
This search for the best change in route that will eliminate the risk of collision following a reported traffic conflict is a difficult task implying a sudden increase in the work of the crew at a very time when it has to increase its vigilance and carry out both visual and radio monitoring at the same time to locate and make contact with the threatening aircraft. Assistance from the aircraft flight management computer would then be welcome.
There are onboard flight management computers capable of making in-flight modifications of the initially planned route. This is done for the avoidance, in the horizontal or vertical planes, of a zone that is belatedly recognized to be dangerous, for example a stormy zone, and it is done at minimum cost in terms of consequences for the mission of the aircraft. However, these flight management computers use methods to determine the avoidance path that are not suited to the circumventing of a zone that is moving at high speed as in the case with the zone that surrounds another aircraft.
The present invention is therefore aimed at a method for the preparation of an avoidance path in the horizontal plane for an aircraft, with a view to resolving a traffic conflict with another aircraft, this method being efficient while causing the least possible disturbance to the goals of the initially planned mission, especially in terms of delay, comfort and consumption, and being easily integrated into the initially planned route for automatic tracking by the navigation and control systems of the aircraft, in order to simplify the work of the aircraft crew and considerably reduce the increase in workload that the crew undergoes in the event of an warning of a risk of medium-term collision with other aircraft.
An object of the invention is a method for the preparation of an avoidance path in a horizontal plane, for a first aircraft following a first route called an initial route, in order to resolve a conflict of traffic with a second aircraft following a second route that may be identical to the first route, on the basis of knowledge of a minimum safety distance S to be maintained between two aircraft, and of the positions X1 and X2 and of the horizontal speed vectors {right arrow over (V1 )} and {right arrow over (V2 )} of the two aircraft, said method comprising the following steps:
the determining of the horizontal speed vector {right arrow over (Vrel )} of the second aircraft relative to the first aircraft,
the determining, in the horizontal plane, of a circle of protection C1 around the first aircraft with the minimum safety distance S as its radius,
the testing of the intersection of the straight line bearing the horizontal speed vector {right arrow over (Vrel )} of the second aircraft with respect to the first one, with the circle of protection C1 of the first aircraft, and
in the event of the intersection of the circle of protection of the first aircraft by the horizontal speed vector {right arrow over (Vrel )} of the second aircraft relative to the first aircraft, implying a risk of collision, namely a tendency for the separation distance between the two aircraft to get reduced until it goes below the minimum safety distance S,
the determining of the angle {right arrow over (xcex1b )}-{right arrow over (xcex1c )} at which the second aircraft perceives the circle of protection C1 of the first aircraft,
the determining of a start-of-avoidance-maneuver point PSOM located on the initial route of the first aircraft and shifted downline from the current position X1 of the first aircraft,
the determining of at least one value of heading angle {right arrow over ("THgr"1b )} and/or {right arrow over ("THgr"1c )} to be followed by the first aircraft, without changing the horizontal speed modulus, to bring the horizontal speed vector {right arrow over (Vrel )} of the second aircraft relative to the first aircraft at most on one of the sides {right arrow over (X2b)}, {right arrow over (X2c)}, of the angle at which the second aircraft perceives the circle of protection C1 of the first aircraft,
the determining of at least one collision-risk avoidance path for the first aircraft comprising a first evasive path constituted by a rectilinear segment having the start-of-avoidance-maneuver point PSOM as its point of origin, one of the new values of heading angle "THgr"1b or "THgr"1c obtained at the previous step as its heading and having, as its end, a rotating point PT chosen beyond a point CPA1 where the separation distance between the two aircraft passes through a minimum value equal to a minimum safety distance S, and, beyond the rotating point PT, a second homing path to the initial route.
Advantageously, the step for determining at least one new value of heading angle comprises:
a test on the oriented angle {right arrow over (xcfx86c )} existing between, firstly, the horizontal speed vector {right arrow over (V2 )} of the second aircraft and, secondly, that side {right arrow over (X2c)} of the sides {right arrow over (X2b)}, {right arrow over (X2c)} of the angle at which the second aircraft perceives the circle of protection C1 of the first aircraft, whose orientation is at the greatest distance from that of the horizontal speed vector {right arrow over (V2 )} of the second aircraft:
{right arrow over (xcfx86c )}=({right arrow over (V2 )}, {right arrow over (X2c )})
xe2x80x83said test consisting in verifying the inequality:       "LeftBracketingBar"          sin      ⁢              xe2x80x83            ⁢                        ϕ          c                →              "RightBracketingBar"     less than             "LeftDoubleBracketingBar"                        V          1                →            "RightDoubleBracketingBar"              "LeftDoubleBracketingBar"                        V          2                →            "RightDoubleBracketingBar"      
xe2x80x83and,
if this inequality is not verified,
the determining of a single value of heading angle {right arrow over ("THgr"1b )} to be followed by the first aircraft, without changing the modulus of its horizontal speed vector to bring the horizontal speed vector {right arrow over (Vrel )} of the second aircraft relative to the first aircraft to the side {right arrow over (X2b)} of the angle at which the second aircraft perceives the circle of protection C1 of the first aircraft, whose orientation is the closest to that of the horizontal speed vector {right arrow over (V2 )} of the second aircraft.
if this inequality is verified,
the determining of two new values of heading angle {right arrow over ("THgr"1b )} and {right arrow over ("THgr"1c )} to be followed by the first aircraft, without changing its horizontal speed modulus to bring the horizontal speed vector {right arrow over (Vrel )} of the second aircraft relative to the first aircraft to one of the sides {right arrow over (X2b)}, {right arrow over (X2c)}, of the angle at which the second aircraft perceives the circle of protection C1 of the first aircraft, one aircraft on one side {right arrow over (X2b)}, the other on the other side {right arrow over (X2c)}.
Advantageously, if more than one new value of heading angle {right arrow over ("THgr"1b )} and {right arrow over ("THgr"1c )} to be followed by the first aircraft, without changing its horizontal speed modulus to bring the horizontal speed vector {right arrow over (Vrel )} of the second aircraft relative to the first aircraft to one of the sides {right arrow over (X2b)}, {right arrow over (X2c)} of the angle at which the second aircraft perceives the circle of protection C1 of the first aircraft, have been determined during the step for determining at least one new value of heading angle, the step for determining at least one avoidance path consists of the determining of two avoidance paths, one for each of the two new values of heading angle {right arrow over ("THgr"1b )} and {right arrow over ("THgr"1c )}.
Advantageously, when the method for preparing an anti-collision avoidance path in the horizontal plane comprises a step for determining at least one avoidance path leading to the determining of more than one avoidance path, the method is supplemented by an additional step for the selection of the avoidance path to be implemented, consisting in making a choice, from among the avoidance paths, of the path that minimizes the lengthening of the initial route of the first aircraft.
Advantageously, the second homing part for homing into the initial route of an avoidance path starts, from the rotating point PT marking the end of the first evasive part of this avoidance path, with a rectilinear segment following a new heading which, with respect to the heading of the initial route, has an angular divergence opposite to that of the rectilinear segment of the first evasive part of said avoidance path.
Advantageously, when the second homing part of the initial route of an avoidance path starts with a rectilinear segment, the rotating point PT that makes the transition, within said avoidance part, between the end of the rectilinear segment of the first evasive part and the rectilinear segment starting the second homing part of the initial route, is chosen, on the rectilinear segment of the first evasive part, so that it is sufficiently distant from the point CPA1 where the separation distance between the two aircraft passes through a minimum equal to the minimum safety distance S so that the separation distance between the two aircraft does not go below the minimum safety distance S during the journey, by the first aircraft, on the rectilinear segment starting the second homing part of said avoidance path.
Advantageously, the modulus of the half-angle or ∥{right arrow over (xcex1b )}∥ or ∥{right arrow over (xcex1c )}∥ at which the second aircraft perceives the circle of protection C1 of the first aircraft is deduced from the relationship:       "LeftDoubleBracketingBar"                  α        b            →        "RightDoubleBracketingBar"    =            "LeftDoubleBracketingBar"                        α          c                →            "RightDoubleBracketingBar"        =          arcsin      ⁢              xe2x80x83            ⁢              (                  S                      "LeftDoubleBracketingBar"                                                            X                  1                                ⁢                                  X                  2                                            →                        "RightDoubleBracketingBar"                          )            
Advantageously, a new value of heading angle {right arrow over ("THgr"1j )} to be followed by the first aircraft, without changing the horizontal speed modulus, to bring the horizontal speed vector {right arrow over (Vrel )} of the second aircraft relative to the first aircraft on one of the sides {right arrow over (X2b)} or {right arrow over (X2c)}, called the envisaged side {right arrow over (X2j)}, of the angle at which the second aircraft perceives the circle of protection of the first aircraft, is obtained by means of an angular relationship that links this new value of heading angle INCORPORER{right arrow over ("THgr"1j )} to:
the heading {right arrow over ("psgr")} of the oriented straight line linking the position X1 of the first aircraft to the position X2 of the second aircraft,
the half-angle {right arrow over (xcex1i )} at which the second aircraft perceives the circle of protection C1 of the first aircraft, oriented from the bisector of the angle constituted by the oriented straight line {right arrow over (X2X1 )} linking the position X2 of the second aircraft to the position X1 of the first aircraft, towards the envisaged side {right arrow over (X2j)} of the angle at which the second aircraft perceives the circle of protection C1 of the first aircraft, and
the oriented angle {right arrow over (xcex3j )} made by the envisaged side {right arrow over (X2j)} of the angle at which the second aircraft perceives the circle of protection C1 of the first aircraft, with the new vector {right arrow over (Vij )} sought for the horizontal speed of the first aircraft in order to eliminate a risk of collision,
this angular relationship being expressed by the relationship:
{right arrow over ("THgr"1j )}={right arrow over ("psgr")}+{right arrow over (xcex1j )}+{right arrow over (xcex3j )}+2kxcfx80
it being known that:
k is an integer,
the horizontal speed vector {right arrow over (Vrelj)} of the second aircraft with respect to the first aircraft, when it travels through the envisaged side {right arrow over (X2j)} of the angle at which the second aircraft perceives the circle of protection C1 of the first aircraft, is equal to the difference between the horizontal speed vector {right arrow over (V2 )} of the second aircraft and the vector sought {right arrow over (V1j)} for the horizontal speed of the first aircraft which, by assumption, has the same modulus as the horizontal speed vector {right arrow over (V1 )} of the first aircraft:   (                                                        V              rel              j                        →                    =                                                    V                2                            →                        -                                          V                1                j                            →                                                                                "LeftDoubleBracketingBar"                                          V                1                j                            →                        "RightDoubleBracketingBar"                    =                      "LeftDoubleBracketingBar"                                          V                1                            →                        "RightDoubleBracketingBar"                                "AutoRightMatch"
the half-angle {right arrow over (xcex1j )} at which the second aircraft perceives the circle of protection C1 of the first aircraft, oriented from the bisector of the angle constituted by the oriented straight line {right arrow over (X2X1 )} linking the position X2 of the second aircraft to the position X1 of the first aircraft, towards the envisaged side {right arrow over (X2j)} of the angle at which the second aircraft perceives the circle of protection C1 of the first aircraft, has the value:             α      j        →    =            ±      arcsin        ⁢          xe2x80x83        ⁢          (              S                  "LeftDoubleBracketingBar"                                                    X                1                            ⁢                              X                2                                      →                    "RightDoubleBracketingBar"                    )      
the oriented angle {right arrow over (xcex3j )} made by the envisaged side {right arrow over (X2j)} of the angle at which the second aircraft perceives the circle of protection C1 of the first aircraft, with the new vector {right arrow over (V1j)} sought for the horizontal speed of the first aircraft in order to eliminate a risk of collision, is expressed as a function of the angle {right arrow over (xcfx86j )} oriented between, firstly, the horizontal speed vector {right arrow over (V2 )} of the second aircraft, and, secondly, the envisaged side {right arrow over (X2j)} of the angle at which the second aircraft perceives the circle of protection C1 of the first aircraft, by the relationship:             γ      j        →    =      arc    ⁢          xe2x80x83        ⁢    sin    ⁢          xe2x80x83        ⁢          (                                    "LeftDoubleBracketingBar"                                          V                2                            →                        "RightDoubleBracketingBar"                                "LeftDoubleBracketingBar"                                          V                1                            →                        "RightDoubleBracketingBar"                          ⁢                  xe2x80x83                ⁢        sin        ⁢                  xe2x80x83                ⁢                  (                                    ϕ              j                        →                    )                    )      
(An absence of definition of the arcsine signifying an impossibility of determining the new value of heading angle {right arrow over ("THgr"1j )} sought.)
xe2x80x83and
the oriented angle {right arrow over (xcfx86j )} between, firstly, the horizontal speed vector {right arrow over (V2 )} of the second aircraft, and, secondly, the side envisaged {right arrow over (X2j)} of the angle at which the second aircraft perceives the circle of protection C1 of the first aircraft, is expressed by the relationship:
{right arrow over (xcfx86j )}={right arrow over ("psgr")}+{right arrow over (xcex1j )}xe2x88x92{right arrow over (xcex82 )}+xcfx80+2kxcfx80
xe2x80x83the oriented angle {right arrow over (xcex82 )} being the heading of the second aircraft.
Advantageously, when the second homing part of an avoidance path starts with a rectilinear segment, the rotating point PT linking the rectilinear segment of the first evasive part and the rectilinear starting segment of the second homing part of an avoidance trajectory is chosen so as to be reached by the first aircraft after a minimum period of time equal to:       t    cpa    =      -          (                                    (                                                            X                  1                                ⁢                                  X                  2                                            →                        )                    ⁢                      xe2x80x83                    ⁢                      (                                                            V                  2                                →                            -                                                V                  1                  n                                →                                      )                                                "LeftDoubleBracketingBar"                                                            V                  2                                →                            -                                                V                  1                  n                                →                                      "RightDoubleBracketingBar"                    2                    )      
{right arrow over (V1n)} being the horizontal speed vector of the first aircraft when it travels through the first evasive part of its avoidance trajectory.
Advantageously, when the second homing part of an avoidance trajectory starts with a rectilinear segment, the distance DCPA1 which, on the rectilinear segment of the first evasive part of an avoidance trajectory of the first aircraft, separates the position CPA1 where the first aircraft perceives its distance from the second aircraft reach a minimum equal to the minimum safety distance S, from the position PSOM of the beginning of the avoidance trajectory is drawn from the relationship:
DCPA1=tcpaxc3x97∥{right arrow over (V1 )}∥
with:       t    cpa    =      -          (                                    (                                                            X                  1                                ⁢                                  X                  2                                            →                        )                    ⁢                      xe2x80x83                    ⁢                      (                                                            V                  2                                →                            -                                                V                  1                  n                                →                                      )                                                "LeftDoubleBracketingBar"                                                            V                  2                                →                            -                                                V                  1                  n                                →                                      "RightDoubleBracketingBar"                    2                    )      
{right arrow over (V1n)} being the horizontal speed vector of the first aircraft when it follows the rectilinear segment of the first evasive part of its avoidance trajectory.
Advantageously, when the second homing part of an avoidance trajectory starts with a rectilinear segment, the distance DPT which, on the rectilinear segment of the first evasive part of the avoidance trajectory of the first aircraft, separates the position CPA1 where the first aircraft perceives its distance from the second aircraft reach a minimum equal to the minimum safety distance S, from the rotating point PT marking the end of the rectilinear segment of the first part of an avoidance path, is drawn from the relationship:             D      PT        =                  t        PT            xc3x97              "LeftDoubleBracketingBar"                              V            1                    →                "RightDoubleBracketingBar"                  with    ⁢          :                  t      PT        =          S      xc3x97      tan      ⁢              xe2x80x83            ⁢              (                                                            χ                EOM                            →                        xc3x97                          (                                                                    ψ                    SOM                                    →                                +                π                +                                                      α                    SOM                                    →                                            )                                2                )            xc3x97              1                  "LeftDoubleBracketingBar"                                                    V                2                            →                        -                                          V                                  1                  ⁢                                      xe2x80x83                                    ⁢                  SOM                                            →                                "RightDoubleBracketingBar"                    
it being known that:
{right arrow over ("khgr"EOM )} is the heading of the relative speed vector of the second aircraft with respect to the first aircraft when the first aircraft embarks on the rectilinear segment starting the second evasive part of its avoidance trajectory,
{right arrow over ("psgr"SOM )} is the heading of the oriented segment linking the position of the first aircraft with that of the second aircraft when the first aircraft is at the starting point PSOM of the first evasive part of its avoidance trajectory,
{right arrow over (xcex1SOM )}, previously named {right arrow over (xcex1b )} or {right arrow over (xcex1c )}, is the half-angle at which the second aircraft perceives the circle of protection C1 of the first aircraft while the first aircraft is at the starting point PSOM of the first evasive part of its avoidance path, this half-angle being oriented from the oriented segment, linking the position of the second aircraft to that of the first aircraft, towards the side of the angle at which the second aircraft perceives the circle of protection C1 of the first aircraft, adopted to obtain passage of the trajectory of the second aircraft relative to the first aircraft, when this first aircraft describes the rectilinear segment of the first evasive part of its avoidance trajectory, and
{right arrow over (V1SOM )} is the horizontal speed vector adopted by the first aircraft when it follows the rectilinear segment starting the second homing part of its avoidance trajectory.